Glaucoma is a disease affecting millions of people in the US alone every year. Elevated intraocular pressure (IOP), the most common cause of glaucoma, slowly kills the ganglion cell axons (which collectively form the optic nerve) affecting the peripheral visual field and progressing to the center. If untreated, glaucoma leads to blindness. In general, visual field loss caused by glaucoma is irreversible.
The usual treatment for glaucoma can be as simple as administering eye drops. Most of current therapies for glaucoma are directed toward decreasing intraocular pressure. Currently recognized categories of drug therapy for glaucoma include: (1) Miotics (e.g., pilocarpine, carbachol, and acetylcholinesterase inhibitors), (2) Sympathomimetics (e.g., epinephrine and dipivalylepinephxine), (3) Beta-blockers (e.g., betaxolol, levobunolol and timolol), (4) Carbonic anhydrase inhibitors (e.g., acetazolamide, methazolamide and ethoxzolamide), and (5) Prostaglandins (e.g., metabolite derivatives of arachindonic acid). Medical therapy includes topical ophthalmic drops or oral medications that reduce the production of aqueous from a ciliary body or increase the outflow of aqueous out of the trabecular meshwork of the eye.
The aqueous or aqueous humor is a transparent liquid that fills the region (anterior chamber) between the cornea at the front of the eye and the lens. The aqueous humor is constantly secreted by the ciliary body around the lens, so there is a continuous flow of the aqueous humor from the ciliary body to the eye's anterior chamber. The eye's pressure is determined by a balance between the production of aqueous and its exit through the trabecular meshwork and Schlemm's canal (major route) or via uveal scleral outflow (minor route).
There are a number of external eye pressure measuring devices. All devices indent the cornea to measure pressure and they do so directly by contacting it or indirectly by a non-contact method (i.e., pneumatic displacement “air puff”). For example, a Tono-pen manufactured by Medtronic Solan (Jacksonville, Fla.) utilizes micro strain gage technology with battery power and a 1.5 mm transducer tip to gently contact the cornea and display the average of four independent readings along with a statistical coefficient. Both contact and non-contact tonometers are very dependent on the eye wall and corneal rigidity and can be grossly wrong because these factors are not taken into account. In addition to the problems of imprecision with most of the external IOP measuring devices, at least the contact ones can only be administered in physicians' offices.
More realistic IOP measurements can be obtained from within the eye. For this purpose a variety of devices have been either proposed or developed recently. However, none of the micromachined devices are being used as a standard method to measure IOP because they are too invasive to be implanted and/or have not been validated in a realistic variable pressure environment (e.g., in an animal eye).
U.S. Pat. No. 6,579,235 issued on Jun. 17, 2003, the entire contents of which are incorporated herein by reference, discloses a device for passively measuring intraocular pressure of a patient including an in vivo sensor and an instrument external to the patient for remotely energizing the sensor, thereby permitting the instrument to determine the intraocular pressure. The device directly and continuously measures the intraocular pressure of a patient. The in vivo sensor in the intraocular pressure monitor includes a capacitive pressure sensor and an inductive component. An instrument, external to the patient, measures the pressure, provides readout of the pressure values and determines the intraocular pressure.
U.S. Pat. No. 6,602,192 issued on Aug. 5, 2003, the entire contents of which are incorporated herein by reference, discloses a non-contact type tonometer monitoring the rate of change in pressure between a standard curve and a measured curve and calculating an intraocular pressure of the patient's eye based on the amended pressure changing curvature.
U.S. Pat. No. 6,537,215 issued on Mar. 25, 2003, the entire contents of which are incorporated herein by reference, discloses a non-contact type tonometer including a compressed air blowing unit that blows the compressed air to a cornea of an examinee's eye; an optical system which projects light to the cornea; a photosensor which detects reflection light reflected from the cornea; and a controller which obtains a change in pressure for a predetermined time based on detection results by the pressure sensor when the photosensor detects a predetermined change amount of the reflection light.
U.S. Pat. No. 6,524,243 issued on Feb. 25, 2003, the entire contents of which are incorporated herein by reference, discloses an applanation tonometer for measuring pressure within a human eye comprising an electrical measurement apparatus which detects the mechanical displacement of a plunger, the displacement of the plunger reflecting an intraocular pressure, and the electrical measurement apparatus converting the corresponding mechanical displacement of the plunger into an electrical signal and display.
U.S. Pat. No. 6,447,449 issued on Sep. 10, 2002, the entire contents of which are incorporated herein by reference, discloses a tonometer sensor for disposition in proximity to a portion of a surface of the eye comprising a substrate including a contact surface for making contact with the surface portion of the eye. The contact surface includes an outer non-compliant region and an inner compliant region fabricated as an impedance element that varies in impedance as the inner region changes shape. A first region of material is responsive to a non-invasive external force to press the contact surface against the surface portion of the eye and cause the compliant region to change shape in proportion to an intraocular pressure of the eye. A second region of conductive material is electrically coupled to the impedance element of the compliant region and is responsive to an external signal for energizing the impedance element so that the intraocular pressure is determined.
U.S. Pat. No. 6,443,893 issued on Sep. 3, 2002, the entire contents of which are incorporated herein by reference, discloses a device for measuring intraocular pressure comprising: a remote measuring device adapted to be implanted in an eye, the remote measuring device having a pressure sensor, a converter for converting sensor signals into information for wireless transmission, and a transmitter; a receiver adapted to be located outside the eye for receiving information transmitted by the transmitter; and an evaluation device for converting information received into data expressing the intraocular pressure and for recording the data, wherein the remote measuring device further includes a data logger in which measurement data continuously supplied by the pressure sensor is stored and from which the measurement data is called up at certain times in operation of the converter.
None of the above-cited prior art discloses an optically powered and optically data-transmitting wireless intraocular pressure sensor, suitable for being implanted in the eye and for monitoring the IOP continuously or on demand. Moreover, none of the above-cited prior art discloses a solar cell system-powered or battery-powered wireless intraocular pressure sensor. Therefore, these aspects of the present invention provide a wireless intraocular pressure sensor (WIPS) that enables detecting IOP violating a predetermined pressure threshold.